Field of the Invention
This invention relates to power over Ethernet cable arrangements. More particularly, this invention relates to active cooling arrangements for power over Ethernet arrangements.
Description of Related Art
A recent development in communications cabling is the tandem delivery of power and data signals through a single cable. Although not always the case, a typical arrangement would utilize a normal LAN (Local Area Network) twisted pair cable, usually having four twisted pairs of insulated copper conductors therein. In normal LAN operations all four pairs are for data communication. However, in tandem power/data applications some of the pairs are dedicated to data communications but one or more of the pairs can be used to deliver power though the same cable. In some cases, a twisted pair carrying data can also carry power at the same time as the data transmits via AC (alternating current) and the power transmits via DC (direct current) so it is possible to split the power and data signals from one another as needed. Such data/power tandem arrangements can be used for example with security cameras or VoIP phones which require a small amount of power as well as data communication.
Initially, IEEE (Institute for Electrical and Electronics Engineers) adopted the 802.3af standard for Power over Ethernet (Or PoE) which has been widely accepted in the industry setting the relevant parameters, such as wattage, negotiation parameters/routines, DC loop resistance etc. . . . , for delivering power in tandem with data. The total amount of power that can be delivered under this standard is 12.95 W which is adequate for such basic applications such as the standard VoIP phones and security cameras noted above.
However, growing lists of features on devices that are connected and powered with tandem power/data cables as well as new communication equipment that likewise can make use of the tandem power/data through LAN cables, has necessitated even more power throughput allowance. IEEE 802.8at is an updated standard that allows for an increase to 25.5 W power (PoE+) to be delivered through such tandem cables. Another even newer standard is IEEE 802.3bt that sets the parameters for using all four twisted pairs to simultaneously send data and power. In the conditions according to this newer standard, cables sending both data and power in some cases will be delivering as much as 100 Watts. These high rates of power transmission can lead to the operating temperatures of the cable exceeding its maximum allowable operating temperature according to the cables own heat tolerance thresholds. This is especially true when large numbers of cables are installed together or bundled adjacent to and abutting one another. Such excessive heat generation is not only a fire hazard, but also the prolonged heating causes a degradation of the cable materials (e.g. jackets, pair insulation etc. . . . ) faster than under normal signal transmission only conditions.
With this increase in power throughput through one or more of the twisted pairs of a LAN cable, there is a corresponding increase in heat that needs to be dissipated from the cables to the environment. This leads to concerns about fire safety and data transmission performance and ultimately limits the number of such tandem operation cables that can occupy a single pathway or be arranged next to one another in order to stay within the range of safe operating temperatures. For example the NFPA (National Fire Protection Association) 70 standard, setting the National Electrical Code covering these cables, requires that the cables do not exceed their listed maximum operating temperature which is typically 60 C.
As shown in prior art FIGS. 1 and 2, typical LAN cables are constructed having four insulated twisted pairs, an optional cross filler (depending on the data signal requirements), and an outer jacket enclosing the cable. The prior jackets for twisted-pair cables do not take heat dissipation into consideration, and therefore, are not optimized for supporting power provided through one or more of its twisted pairs. Standard cable jackets such as those shown in FIGS. 1 and 2 possess an outer surface that generally maintains an equal distance from the center of the cable for the entire length of the cable. When multiple LAN cables are placed together they touch along their entire longitudinal axis (longest axis) and entrap the heat generated by the power conductors as conductive heat transfer is less efficient than convective heat transfer.
In the related U.S. patent application Ser. No. 15/204,583, and as shown in FIGS. 3 and 4, one arrangement is provided where the jackets of the cables, used in power over Ethernet applications have a series of ridges or valleys disposed, circumferentially or helically around the outer surface of the cable jacket. Such ridges or valleys are spaced apart from one another over the length of the cable. These structures, either ridges or valleys generate an air gap between adjacent cables allowing air to flow between, allowing the heat released from the one or more powered twisted pairs to escape more easily through the outer surface of the jacket and to generate a convection air flow upward around and in between the cables.